Method and apparatus for controlling operation of a centrifugal



Apnl 7, 1970 D. M. THOLL ET AL 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL FiledFeb. 12, 1968 5 Sheets-Sheet 1 Daarzid 772 -TirozZ Ezzaecif J 2%,

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p 1970 D. M. THOLL E L 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL 1 FiledFeb. 12, 1968 5 Sheets-Sheet 5 April 7, 1970 THOLL ET AL 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL 5Sheets-Sheet 4 353 M E RH QMV Aprll 7, 1970 M, THOLL ET Al. 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL FiledFeb. 12, 1968 5 Sheets-Sheet 5 Ea mi) Jaime,

United States Patent C) 3,504,794 METHOD AND APPARATUS FOR CONTROLLINGOPERATION OF A CENTRIFUGAL David M. Tholl, Cumberland, R.I., and ErnestJ. Zltke, Brockton, Mass., assignors, by mesne assignments, to The DeLaval Separator Company, Poughkeepsie, N.Y., a corporation of New JerseyFiled Feb. 12, 1968, Ser. No. 704,808

Int. Cl. B04b 13/00 US. Cl. 210-78 Claims ABSTRACT OF THE DISCLOSURE Arotatable centrifuging basket apparatus having variable speed powerdriving means is regulated by a speed sensing apparatus arranged tocontinuously sense changes in rotative speed of the basket. The sensingapparatus is particularly designed to operate at relatively low rotativespeeds at which the basket is driven when moved into engagement with ascraper blade or plow for removing caked material from the innerperipheral surface of the basket at the end of a centrifuging cycle. Thesensing device controls speed stabilizing means for adjusting the powerdriving means in response to change in basket speed within a specificrange to increase power driving forces and maintain the basket at aproper rotative speed for carrying out the plowing operation withoutdanger of stalling or causing excessive wear of the equipment.

This invention relates in general to centrifugals and, moreparticularly, to a method and apparatus for controlling the operation ofa variable speed centrifugal. Machines of the variable speed classindicated include a curb, a basket rotatably supported in the curb, andpower driving means for driving the basket at selected speeds, includinga loading speed, a relatively high spin or centrifuging speed, and arelatively low plow speed for enabling a scraper blade or plow to removecaked material collected on the inner peripheral surface of the basketduring removal of the liquid material.

In dealing with some mixtures which are required to be centrifuged,displacement of liquid material through the perforated basket of thecentrifugal is accompanied by the accumulation of a layer or cake ofsolid material in the mixture. This cake may become quite firmly packedagainst the inner peripheral surface of the basket. An adjustablescraper or plow member is commonly used to remove the cake at the end ofthe centrifuging cycle and must be used with the basket slowed to arelatively low plowing speed.

The resistance of the cake to displacement by the plow may vary and, inmany instances, may build up rapidly to exert sudden torque forces onthe power driving means for the basket. Such torque forces can induceexcessive wear and in some cases may cause slowing down of the baskettoa point where it becomes stalled, thus resulting in loss of time andlowered efficiency.

Operation of centrifugals may also be of a somewhat hazardous naturewhen explosive mixtures are being processed. As is frequently the casethis imposes limitations on the use of some forms of electrical controlswhere the danger of accidental sparks may be present.

It is, in general, a chief object of the invention to improve operationof variable speed centrifugals. The invention is also concerned with theproblems indicated in connection with operating a centrifugal atrelatively low plowing speeds to remove caked mate-rial.

Another specific object of the invention is to devise a speedstabilizing control apparatus which can be used to regulate the speed ofa basket during plowing operations so that a sudden build-up in torqueload will not unduly reduce speed of the basket or cause it to becomestalled.

Still another specific object of the invention is to provide speedstabilizing control apparatus which can be safely used in processingexplosive mixtures and which is capable of operating automatically andwhich can be conveniently and quickly installed on standard types ofCentrifugals.

The invention and its other objects and novel features will be morefully understood and appreciated from the following description ofpreferred embodiments selected for purposes of illustration and shown inthe accompanying drawings in which:

FIGURE 1 is a plan view of a centrifugal with which is associated ahydraulic motor and a separately located hydraulic pump apparatus foractuating the hydraulic motor, together with electrical control devices;

FIGURE 2 is a cross section taken on the line 22. of FIGURE 1;

FIGURE 3 is a diagrammatic view further illustrating the apparatus shownin FIGURE 1 and more particularly indicating electric control means insuitably connected relationship;

FIGURE 4 is a wiring diagram for air control means for the centrifugalapparatus shown in FIGURE 1; and

FIGURE 5 is a diagrammatic view illustrating a modified form of electriccontrol apparatus.

From a consideration of the torque problem described above, we havedevised a novel method for realizing the objectives outlined byutilizing metered changes in rpm. in the motor means employed to drivethe basket of a centrifugal during the period when a plowing operationis in progress. The invention in one preferred embodiment therefore willbe described with reference to measuring changes in the -r.p.m. of ahydraulic motor operated by a hydraulic pump and suitable control valveapparatus for the pump.

In a typical centrifuging operation using a hydraulic system of thisclass the hydraulic motor may drive the basket at a load speed of, forexample 600 rpm. When loading is completed, the rotative speed of thebasket is increased to a spin speed of 1100 rpm. for instance and rununtil the product is satisfactorily centrifuged. Thereafter the basketis slowed to a plow speed of approximately 50 rpm.

In one preferred embodiment the method and apparatus of the invention isparticularly concerned with stabilizing the plowing speed and, inparticular, with preventing any appreciable drop in plow speed below 50rpm. during the period of operation in which plowing is required to becarried out. It will, however, be understood that the invention is notlimited to this or any other particular operating speed or variationthereon.

Considering in further detail the method of stabilizing plow speed tomaintain approximately 50 rpm. during period when excessive torque loadsmay be anticipated in removing cake from a centrifugal basket we mayemploy, for example, a centrifugal of well-known construction includinga curb 2 having a bottom 3 solidly supported on a base of suitablenature. The bottom of the curb is formed with a discharge opening 4. Atits upperside the curb 2 is constructed with a top section 6 bolted asat 8 and having a central section through which is rotatably mounted avertical driving shaft mechanism 10 in a suitable bearing means 12.

Secured around the driving shaft 10 is a basket 14 constructed in theusual manner with perforations as 16 through which liquid materialintroduced into the basket may pass and drop down through the opening 4of curb 2. The driving shaft 10 is powered by a. hydraulic motor 18 in abearing mount 20'.

Also located through the top section 6 of the curb at one side of thedrive shaft 10 is a pivoting plow apparatus including a scraper blade orshoe 22 supported on a shaft 24 which is adjustable about a verticalaxis by means of a pneumatic cylinder 26. The cylinder 26 when engagedoperates to swing the shoe 22 into and out of engagement with the innerperipheral surface of the basket 14.

A tachometer 28 is provided at the upper side of the hydraulic motor 18in the conventional manner to measure rotative speed of the motor 18 andelectrically connected to the tachometer is a speed or meter indicator30 which is indicated diagrammatically in FIGURE 3.

At a point removed from the curb 2 is located a hydraulic pump 32 alsoshown in FIGURE 3 and driven by electric motor 33. The pump 32 isconnected to hydraulic motor 18 by conduits 34 and 36. These conduitsconduct hydraulic fluid into and out of the hydraulic motor from ahydraulic fluid supply 40. The hydraulic pump 32 is regulated by meansof a spring-loaded pneumatically operated actuator or throttle device 42which is connected to a source of compressed air 44 (FIGURE 3) through aseries of control valves. Other forms of positioning devices may also beemployed.

As indicated diagrammatically in FIGURE 4, the control valves areoperated by solenoid devices electrically connected to operate in apredetermined sequence under the control of electrical relay controlmeans as indicated diagrammatically at the upper right hand side of FIG-URE 4.

In a typical machine operation a pressure range of from 3 psi. to psi.may be supplied from a source of compressed air 44 (FIGURE 3), and thissource of compressed air is connected by suitable conduit means throughthe solenoid control valves shown in FIGURES 3 and 4 to regulate thespeed of hydraulic pump 32.

In starting a centrifuging operation the electrical motor 33 (FIGURE 3)is energized and drives pump 32 in turn delivering hydraulic fluid tohydraulic motor 18 at some desired rate controlled by the setting ofvalve means as determined by the electrical relay control means referredto above, and shown at the upper right hand side of FIG- URE 4.

Preferably the controls are first set to bring the machine up to aloading speed of approximately 600 rpm. by operating solenoid 48. Whenthe machine reaches this loading speed the valve mechanism furnishes apressure of approximately 7 p.s.i. to the throttle device 42 of thehydraulic pump 32 and a relay opens a feed valve for introducingmaterial into the basket 14. Loading of material into the basket thencontinues until a predetermined depth of material is reached at whichpoint loading is interrupted by suitable switch limit means. Thereuponvalve 48 is opened and valve 50 is closed to provide a spin speed ofsome desired value. As a result of the valve being energized by the spinspeed solenoid indicated a pressure of approximately 15 psi. is exertedthrough the throttle device 42 providing, for example, a spin speed ofabout 1,100 rpm.

The electrical control means continues to time the duration of the spinoperation and at a desired point the spin speed solenoid and valve 50are operated and an exhaust solenoid opens the exhaust valve 53. Whenthe machine reaches a speed of a predetermined lesser rpm. theelectrical control means operates a relay for re-energizing the exhaustsolenoid 53 and also energizes the plowing speed solenoids and valves 46and 47 to furnish a pressure of approximately four p.S.i. This producesa plow speed in motor 18 of about 50 to 60 rpm.

The present invention, as earlier indicated, combines with theconventional operations described a method and means for stabilizingplow speeds in a range of from 50 to 60 rpm. In carrying out thisprocedure we continuously regulate the position of the throttle device42 in response to changes in speed of motor 18 within the selected rangeof plow speeds of from 50 to 60 rpm. This is accomplished by interposingin the compressed air lines, which is selectively set to deliver apressure of 4 p.s.i. to throttle device 42, an adjustable air valve ofthe flapper type which is indicated in FIGURE 3 diagrammatically bynumeral 66 and which can be opened to increase the pumping pressure inpump 32 whenever a drop in r.p.m. at the motor 18 occurs.

In carrying out this procedure in one preferred embodiment of theinvention, there is combined with the speed regulating apparatus alreadydescribed an adjustable shunt potentiometer which, as shown in FIGURE 3,is electrically connected into the conductor wires leading to the speedindicator 30 so as to sense changes in voltage across the speedindicator.

Sensed changes in voltage modified by the potentiometer 60 are led intoa converter device 62 of a type suitable for changing electromotiveforces to current. The resulting output of current from member 62 iselectrically connected to a transducer device 64 for changing electricalenergy into mechanical movement. This mechanical movement is appliedthrough a pivoting linkage 65 (FIG- URE 3) to adjustably close theposition of a flapper valve 66 located in the plow speed air conduitleading to member 42 in a slightly opened position so as to increasepressure up to approximately seven pounds at the pump thereby producinga speed of about 50 r.p.m.

In operating this stabilizing control apparatus, the plow 22 starts tomove into contact with caked material at the inside of the basket 14 andthe basket at this point is being driven by a hydraulic motor 18 at arange of speeds of from 50 to 60 rpm. As soon as the plow engagesagainst a cake of suflicient resistance to cause the machine to slowdown appreciably, the potentiometer 60, which is in series with the rpm.meter 30, sends an electrical signal to the transducer which adjustablycloses the flapper valve 66 and provides for increasing the pressure tothe pump 32 with the resultant increase in speed of hydraulic motor 18.Immediately upon the hydraulic motor regaining its desired speed of from50' to 60 rpm. the flapper valve 66 adjustably opens to a prior slightlyopened position and operation continues as before. A similar cyclingtakes place thereafter whenever the machine slows down appreciably asindicated by the meter output.

It will be apparent that we may also use additional valve means tocontrol or maintain suitable load and spin speeds when an unusuallyheavy load resistance may suddenly develop in response to an appreciablechange in rpm. above or below a desired predetermined range for eitherof such speeds. In addition, we may desire to vary the location and typeof the adjustable flapper valve 66.

In still another desirable modification of the invention, we may employan apparatus of the class described in FIGURE 5 in which a variablespeed electric motor 72 is employed to drive a basket 70. As noted inFIGURE 5, the basket 70 is suspended below the driving motor 72 which iscontained in an explosion proof housing and electrically connected to anelectrical control circuit consisting of a silicon control rectifier 74located at a removed point at an opposite side of a shield barrier 76.This revents any possible occurrence of sparks coming into contact withan explosive mixture in the basket. The member 74 is operated under thecontrol of a firing circuit device 78 of conventional nature responsivein turn to change in electrical signals from a transducer 80, alsoexternally located with respect to barrier 76. This transducer 80includes a pneumatically displaced element connected to an air line 82and this air line 82 has connected therein a flapper valve 84 which isarranged to regulate flow of compressed air through the line in responseto changes in speed of motor 72 as regulated by a pneumatic tachometer86.

By means of this arrangement it will be apparent that the speed of theelectric motor 72 may be regulated in accordance with a change inr.p.rn. resulting from engagement of a plow member with caked materialin the basket apparatus 70 and any drop in r.p.m. of appreciable naturewill result in the wiring circuit acting through the silicon controlrectifier 74 increasing the motor speed and overcoming caked resistancealmost instantly. It will also be evident that by means of the methodand apparatus of the invention a more efficient centrifuging operationmay be carried out, particularly with respect to the removal of cake. Bycompensating for torque load in the manner described, a greatlysimplified discharger shoe operation may be carried out with onedischarger blade making a single cut into the caked material instead ofhaving to be utilized to make a number of cuts at progressively lowerlevels as is now the practice in many cases.

We claim:

1. In a method of centrifuging the steps which include containing amixture of liquid and solid material in a perforated basket which ismounted for rotative movement in a curb member and actuated by variablespeed power driving means, subjecting the mixture to centrifugal forcesexerted at relatively high rotative speed of the basket whereby theliquid component is centrifugally displaced through the perforatedbasket and solid material is collected on the inner peripheral surfaceof the basket in the form of a hard layer of cake, reducing the rotativespeed of the basket to a redetermined value by controlling the saidpower driving means, then engaging the inner periphery of the relativelyslowly rotating basket and the said layer of caked material against acake displacing plow whereby the caked material is displaced with torqueforces being induced tending to slow down the rotating basket, sensingchanges in basket speed, and continuously regulating the power drivingmeans in response to sensed changes in rotative speed of the basket bysaid torque forces to maintain the basket in rotative operation whilethe caked material is being removed.

2. A method according to claim 1 in which change in rotative speed ofthe basket induced by said torque forces is electrically sensed and thepower driving means is regulated in accordance with the electricallysensed changes.

3. A method according to claim 2 in which the power driving meansconsists of a hydraulic motor and said electrically sensed changes inbasket speed control the rate of flow of hydraulic fluid supplied to thehydraulic motor.

4. A method according to claim 2 in which the power driving meansconsists of an electrical motor and the electrical sensing changes inbasket speed are automatically transmitted to the said electrical motor.

5. A method according to claim 1 in which the change in rotative speedof the basket is mechanically sensed and the power driving means isregulated in accordance with the mechanically sensing changes.

6. Apparatus for centrifuging a mixture of liquid and solid materialcomprising a curb, a perforated basket mounted for rotative movement inthe crub, a plow in the basket, means mounting the plow for movements toand from an operating position in which the plow is engageable withsolid material caked on the inner periphery of the basket, for plowingthe caked material from said inner periphery, variable speed powerdriving means for rotating the basket at a range of speeds including acentrifuging speed and a relatively low speed at which said plowing iseffected, means for sensing a reduction in said relatively low speed ofthe basket during the plowing, and means responsive to said sensingmeans for increasing power driving forces exerted on the basket tocounteract said sensed reduction of the plowing speed.

7. A structure according to claim 6 in which the power driving meansconsists of a hydraulic motor and the sensing means consists of anelectrically operated mechanism for regulating the speed of thehydraulic motor.

8. A structure according to claim 7 in which the electrically operatedmechanism includes a meter for electrically measuring speed of thehydraulic motor and means for converting electrical measurements intomechanical movement for regulating flow of hydraulic fluid into thehydraulic motor.

9. A structure according to claim 6 in which the means responsive to thesensing means for increasing power driving forces consist in a pump, apressure-regulated valve for controlling the pump and a pneumatic valvedevice operable to change the setting of the pump valve, said pneumaticvalve device being responsive to sensed changes in rotative speed of thebasket.

10. A structure according to claim 6 in which the means responsive tothe sensing means for increasing power driving forces consist in a pump,a pressureregulated valve for controlling the pump and a pneumatic valvedevice operable to change the setting of the pump valve, said pneumaticvalve device being responsive to sensed changes in rotative speed of thebasket, and said means for sensing a change in rotative speed of thebasket including an electrically operated meter for indicatingelectrical voltage changes and means for converting said voltage changesinto current changes.

References Cited UNITED STATES PATENTS 2,461,764 2/1949 Olcott 210-2,667,974 2/1954 Hertrich 210l45 3,152,462 lO/1964 Elliott et al. 210143X 3,262,569 7/1966 Wade et a1. 210-144 I. L. DE CESARE, Primary ExaminerU.S. Cl. X.R.

